Pulmonary surface active material prevents alveolar collapse by lowering surface tension at the air-liquid interface in the distal lung. Surfactant is secreted by alveolar type II cells and is composed primarily of phospholipids and lesser amounts of cholesterol and surfactant associated proteins. The most abundant surfactant associated protein is a glycoprotein of MW 26-38 kDa termed SP-A. A second group of very hydrophobic proteins has been described which consists of at least two different proteins designated SP-B and SP-C. These hydrophobic surfactant associated proteins are biophysically, chemically and physiologically important constituents of surfactant. Relatively little is known about the molecular biology of these hydrophobic surfactant associated proteins. Because the rat has proved to be a useful experimental animal model for studying the physiology of surfactant as well as the biology of alveolar type II cells, the proposed research would study the molecular biology of these surfactant associated proteins in the rat. cDNA clones specific for rat SP-B and SP-C will be isolated by screening a rat lung cDNA library with human cDNA clones for SP-B and SP-C. They will then be sequenced to identify domains conserved across species. Development of rat specific cDNA clones will facilitate the study of mRNA production and identification of cells producing these mRNAs. The cells in the lung responsible for producing mRNA for SP-B and SP-C in adult and fetal rat lung will be identified by Northern analysis of isolated cell populations and in situ hybridization of lung tissue. The ontogeny of SP-B and SP-C mRNA transcription will be determined qualitatively by Northern analysis and quantitatively by slot blotting and scanning densitometric analysis. The effects of agents known to affect lung maturation and surfactant production, i.e. corticosteroids, cAMP, insulin, transforming growth factor-Beta and epidermal growth factor on mRNA expression for SP-B and SP-C will be examined by assaying their effects on transcription for these mRNAs in organ cultures of fetal lung and isolated adult type II cells. The relationship of transcription of mRNA for SP-B and SP-C to that of SP-A will be determined.